This invention relates generally to valve trains and more specifically to camshafts as a means to control and vary the timing of poppet valves in internal combustion engines.
Present day internal combustion engines suffer from one very obvious technical defect--the faster the engine turns, the shorter the time the valves remain open, since the camshaft and crankshaft make complete revolutions in a fixed relationship. Obviously, for more efficient engine operation, the reverse would be preferable--valves that remain open at higher speeds (relative to a complete engine revolution), both to ingest the greater volume of fuel-air mixture and to expel the greater density of exhaust gases, while a shorter valve event at lower speeds would serve to curtail power loss and to lessen the emission of unburned hydrocarbons, both of these adverse effects being a result of valves left open overlong. In practice, valve settings are always a compromise--being efficient in some middle range but losing efficiency markedly in the high and low speed ranges.
Prior art discloses many attempts to produce a practical variable valve timing device with which to overcome the described problem, none of which solutions can be deemed successful since it can be shown that modern day valve trains are not variable in operation, and are in fact basically unchanged in operating mode from valve trains of a half century ago, showing only an increased tendency towards overhead arrangements--first as to valves, and more recently as to camshafts.
The reasons for the commercial failure of previously patented variable timing devices are many--overcomplexity, high cost of manufacture, space or weight considerations, but most especially the lack of indicated durability. A common thread in these prior art devices is their heavy reliance on unproven non-standard valve train elements, elements such as fulcrums, frusticonical cams, oscillating cams and wedges, subsidiary camshafts, concentric wheels, hydraulics, belt tensioners, and the like. Furthermore, almost all these prior devices rely on either point contact design or on double cycle components. In point contact designs, somewhere along the valve train, all the considerable pressures of valve train operation are concentrated on a single pin point of contact, resulting inevitably in wear and control problems, while devices which seek to avoid this weakness are usually double cycle in nature--that is, they operate and reverse direction two or more times per camshaft revolution, this also being an unpromising situation in terms of indicated durability.
Avoiding this approach, the present invention draws directly on proven marketplace valve train design, utilizing basically equivilant components in basically equivilant working relationships, reconfiguring such components and relationships only in the minimal amount neccesary to arrive at the intent of this invention--a simple and durable means of making variable the valve event in an internal combustion engine.
The object of the present invention is to provide an improved valve operating mechanism for an internal combustion engine which serves to vary the valve events.
Another object of the invention is to provide an improved camshaft, wormed for a portion of its length, to assist in variably controlling the valve event in an internal combustion engine.
Another object of the invention is to provide a variable cam assembly, said cam assembly splitable into two or more operating parts, said cam assembly to assist in variably controlling the valve event in an internal combustion engine.
Another object of the invention is to provide an efficient means for axially shifting a camshaft.
Another object of the invention is to provide speed sensitive means for variably controlling the valve event in an internal combustion engine.
Another object of the invention is to provide a method whereby a controllable power source may variably alter the valve event in an internal combustion engine, such controllable power source programable to such considerations as engine speed, engine or ambient temperature, engine load, acceleration, decelleration, braking, and exhaust emissions.
Another object of the invention is to increase engine efficiency by the use of paired variable camshafts according to the invention, one such variable camshaft working intake valves only, the second such variable camshaft working exhaust valves only, such paired variable camshafts capable of operating independently or in synchronization.